The present invention relates to a drilling apparatus of a hard brittle material such as ceramics and a method thereof in which a holder having an inner conduit through which lubricant is supplied for cooling and removing chips from a workpiece is used for holding a tool and is sealed to prevent leakage of the internally supplied lubricant during drilling with a core drill, and it also relates to a drilling apparatus of a hard brittle material and a method thereof including a system to detect abnormality by measuring the load from the core drill during drilling. This invention can be applied to drilling technology in the field of various industrial products such as automobiles, electronic devices and so forth which include parts made of hard brittle materials.
In order to drill a hole (especially of a small diameter) in a hard brittle material such as ceramics, machining methods in which diamond is used as abrasive grains are mainly employed. In such machining, floating abrasive grains and fixed abrasive grains are used. The former is used for ultrasonic machining disclosed in, for example, "Machine Technology", Vol. 35, No. 2. However, this ultrasonic machining involves a problem in the relationship between the tool durability for maintaining the accuracy and a decrease in the operation efficiency, and a problem of processing and disposing the abrasive grains in the method of floating abrasive grains. On the other hand, the latter is used for abrasive grinding, and a mounted wheel is a typical example. In this case, however, as the mounted wheel is solid, it is necessary to remove the whole material corresponding to a hole while drilling, and thus, cooling is difficult. Therefore, the mounted wheel has a short durability. A hollow tubular core drill is intended for solving the problem of this mounted wheel (see Japanese Patent Unexamined Publication No. 4-244382). However, in order to utilize the drilling method with such a core drill effectively, three components, i.e., a core drill, a collet chuck for holding the core drill, and a structure for delivering lubricant through their inner conduit must be provided.
In the conventional technology, the machining efficiency in particular has been inadequate for drilling a large number of holes. As for the core drill, there has been no collet chuck which can endure the internally supplied lubricant at a high pressure of 40 kgf/cm.sup.2 when a hard brittle material such as ceramics is drilled.